Plasma film-forming apparatus and cleaning method for the same

ABSTRACT

In a plasma film-forming apparatus which includes a film-forming chamber in which a substrate is arranged, a film-forming gas introducing pipe connected to a supply source of a film-forming gas at its first end, a shower plate through numerous holes of which a second end of said film-forming gas introducing pipe communicate with said film-forming chamber, film-gas exciting means for exciting film-forming gas introduced through said shower plate into said film-forming chamber, to form a film on the surface of said substrate with the chemical reaction, radicals-producing means which excites said cleaning gas and produces radicals, and cleaning-gas introducing means which introduces said cleaning gas containing said radicals into said film-forming chamber, the improvement in which said cleaning-gas introducing means communicate directly with said film-forming chamber.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a plasma film-forming apparatus and acleaning method for cleaning the plasma film-forming apparatus.

[0003] 2. Description of the Prior Art

[0004]FIG. 1 shows a plasma film-forming apparatus 1 of the prior art.It is an apparatus to form a film on a substrate 9 by a plasma CVD(Chemical Vapor Deposition) method. A cathode electrode 4 is arranged onthe upper wall of a vacuum tank 2. An anode electrode 3 is arrangedopposite to the cathode electrode 4, in a film-forming chamber 10 of thevacuum tank 2. The cathode electrode 4 is connected to a high frequencyelectric power source 8. The anode electrode 3 is connected to theearth. It functions also as a supporter for substrate. The substrate 9is mounted on the anode electrode 3.

[0005] The cathode electrode 4 is dish-shaped. A gas-introducing pipe 13is connected to a central hole of the upper wall of the cathodeelectrode 4. A shower plate 5 is fixed to a lower end of the cathodeelectrode 4. Numerous small holes are made in the shower plate 5 whichis facing to the substrate 9.

[0006] One end of a film-forming gas introducing pipe 6 is connected tothe gas-introducing pipe 13. Another end of the film-forminggas-introducing pipe 16 is connected to a not-shown film-forming gassupply source. A radicals producing source 11 is connected to one end ofa gas-introducing pipe 12. Another end of the gas-introducing pipe 12 isconnected to a not-shown cleaning gas sipply source. The radicalsproducing source 11 is further connected to the pipe 13.

[0007] Next, operations of the above described plasma film-formingapparatus 1 will be described.

[0008] For example, there will be described a case of forming a film ofSiNx on the substrate 9. First, the film-forming chamber 10 is evacuatedthrough an exhaust port 7 and so is put under the lower pressure. Forexample, SiH₄ gas and NH₃ gas are introduced onto the shower plate 5through the film-forming gas introducing pipe 6 and the gas introducingpipe 13. They are ejected through the numerous holes of the shower plate5 uniformly into the film-forming chamber 10 and toward the substrate 9.

[0009] Next, a high frequency electric power is supplied to the cathodeelectrode 4 form the high frequency power source 8, to decompose andmake the introduced gases to react on each other gases in thefilm-forming chamber 10. Thus, a film of SiNx is formed on the substrate9.

[0010] The above film-forming operations are repeated, and so SiNx filmsare adhered and piled onto the shower plate 5, anode electrode 3,cathode electrode 4 and inner walls of the vacuum tank 2 besides thesubstrate 9. The SiNx films on the above portions besides the substrate9 should be removed (cleaned).

[0011] Next, there will be described cleaning operations of the interiorof the film-forming chamber 10.

[0012] As on the film-forming operation, the film-forming chamber 10 isevacuated through the exhaust port 7 and so put under the lowerpressure. For example, NF₃ gas is supplied into the radicals producingsource 11. Microwave is applied to the NF₃ gas there, so that fluorinefree radicals are produced there. NF₃ gas including fluorine freeradicals are introduced into the film-forming chamber 10 through thegas-introducing pipe 13 and the shower plate 5.

[0013] Then, fluorine radicals react chemically on the materials (SiNxfilm) to be cleaned. The SiNx films piled on the inner wall of thevacuum tank 2 are removed. The removed SiNx materials are dischargedthrough the exhaust port 7 together with the cleaning gas.

[0014] The method that the radicals for cleaning are thus previouslyproduced and then introduced into the film-forming chamber 10, has theadvantage that the plasma damage of the shower plate 5 is decreased, incomparison with the method that free radicals for cleaning are producedin the film-forming chamber 10 by the high frequency electric powerapplied to the cathode electrode 4 from the high frequency power source8, as on the film-forming operation. introduced into the film-formingchamber 5, most of the radicals are dissipated, since the passing rateof the shower plate 5 having numerous small holes is low. Thus there isthe problem that the cleaning rate is lowered.

[0015] Further, in consideration of the problem that most of theradicals are dissipated through in the shower plate 5, a very highfrequency microwave such as 2.45 GHz is applied to theradicals-producing source 11 to produce more radicals, in some cases.However, such method requires high cost.

SUMMARY OF THE INVENTION

[0016] Accordingly, it is an object of this invention to provide aplasma film-forming apparatus and the cleaning method that thedissipation of the radicals to be introduced into the film-formingchamber can be prevented.

[0017] Another object of this invention is to provide a plasmafilm-forming apparatus and the cleaning method that the radicals as thecleaning gas produced outside the film-forming chamber, can beeffectively used for cleaning the film-forming chamber.

[0018] In accordance with one aspect of the invention, in a plasmafilm-forming apparatus which includes a film-forming chamber in which asubstrate is arranged, a film-forming gas introducing pipe connected toa supply source of a film-forming gas at its first end, a shower platethrough numerous holes of which a second end of said film-forming gasintroducing pipe communicate with said film-forming chamber, film-gasexciting means for exciting film-forming gas introduced through saidshower plate into said film-forming chamber, to form a film on thesurface of said substrate with the chemical reaction, radicals-producingmeans which excites said cleaning gas and produces radicals, andcleaning-gas introducing means which introduces said cleaning gascontaining said radicals into said film-forming chamber, the improvementin which said cleaning-gas introducing means communicate directly withsaid film-forming chamber. film-forming chamber.

[0019] In accordance with another aspect of the invention, in a cleaningmethod of a plasma film-forming apparatus which, in the film-formingoperation, introduces a film-forming gas through a shower plate havingnumerous holes into a film-forming chamber, excites the introduced gasand forms a film, with the chemical reaction, on a surface of substratearranged in said film-forming chamber, and in the cleaning operation,introduces a cleaning-gas containing radicals produced by exciting ofsaid cleaning-gas, into said film-forming chamber and cleans saidfilm-forming chamber by chemical reaction of said radicals and removesmaterials to be cleaned, the improvement in which said cleaning gascontaining said radicals is introduced directly into said film-formingchamber.

BRIFE DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a vertical cross-sectional view of a plasma film-formingapparatus of the prior art;

[0021]FIG. 2 is a vertical cross-sectional view of a plasma film-formingapparatus according to first and second embodiment of this invention;

[0022]FIG. 3 is vertical cross-sectional view of a plasma film-formingapparatus according to a third embodiment of this invention;

[0023]FIG. 4 is a cross-sectional view taken along the line iv-iv inFIG. 3;

[0024]FIG. 5 is a graph for showing the comparisons of the cleaningrates of SiNx films between the prior art and the first embodiment ofthis invention; and

[0025]FIG. 6 is a graph for showing the cleaning rates of SiOx film bythe second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Next, embodiments of this invention will be described withreference to the drawings. The parts corresponding to the parts of theabove prior art are denoted by the same reference numerals, the detaileddescription of which will be omitted.

[0027]FIG. 2 shows a plasma (CVD) film-forming apparatus 20 according toa first embodiment of this invention. A cathode electrode 4 connected toa high frequency electric power source 8 is arranged in the upper wallof a vacuum tank 2. An anode electrode 3 supporting a substrate 9 andconnected to the earth is arranged opposite to the cathode electrode 4in the film-forming chamber 10.

[0028] A film-forming gas introducing pipe 15 is connected to a centralhole of the upper wall of the cathode electrode 4. A shower plate 5having numerous small holes is fixed to the lower end of the cathodeelectrode 4, opposite to the substrate 9.

[0029] A radicals-producing means 21 is arranged outside the vacuum tank2. An input side of the radicals-producing means 21 is connected througha conduit 22 to a not-shown cleaning gas supply source. Theradicals-producing means 21 consists of a chamber for a cleaning gasintroduced from the conduit 22 and a high frequency electric powersource applying a high frequency electric power to the containedcleaning gas in the chamber for producing radicals.

[0030] An output side of the radicals-producing means 21 is connectedthrough a valve 24 to one end of a pipe 23 for introducing a cleaninggas. Another end of the pipe 23 is connected to a hole made in the sidewall of the vacuum tank 2, positioning between the shower plate 5 andthe anode electrode 3. Thus, the pipe 23 for introducing the cleaninggas directly communicates with the inside of the film-forming chamber10.

[0031] In the film-forming operation, the film-forming chamber 10 isevacuated through the exhaust port 7 and is put under the lowerpressure, as in that the prior art. A film-forming gas (SiH₄ gas, NH₃gas) is supplied through the film-forming gas introducing pipe 15 ontothe shower plate 5. It is ejected into the film-forming chamber 10 fromthe numerous small holes of the shower plate 5. A high frequencyelectric power is supplied to the cathode electrode 4 by the highfrequency electric power source 8 to decompose and make the introducedfilm-forming gas reacting. Thus, a film of SiNx is formed on thesubstrate 9.

[0032] In the cleaning operation of the film-forming chamber 10, thefilm-forming chamber 10 is evacuated through the exhaust port 7 and putunder the lower pressure. Then, the cleaning gas such as NF₃ gas issupplied to the radicals producing source 21 to which a high frequencyelectric power (400 kHz) is supplied. Fluorine radicals are produced inthe radicals-producing source 21. The valve 24 is opened to introducedirectly the NF₃ gas containing the fluorine radicals into thefilm-forming chamber 10 through the gas-introducing pipe 23 as the meansfor introducing the cleaning gas. The fluorine radicals react on theSiNx film to be cleaned. Thus, the interior of the film-forming chamber10 is cleaned. Thus, in this embodiment, the radicals pass not throughthe shower plate 5, but directly introduced into the film-formingchamber 10 to be cleaned. Thus, most of the radicals can be preventedfrom dissipating before introduced into the film-forming chamber 10. Thefilm-forming chamber 10 can be effectively cleaned. As shown in FIG. 5,the cleaning rate of the SiNx according to this embodiment is higherabout twenty times than the prior art method in which the radicals passthrough the shower plate 5.

[0033] Further, the micro-wave generator of a high frequency such as2.45 GHz was used for producing radicals in the radicals-producing meansof the prior art. It is very expensive. In the embodiment of thisinvention, it is not necessary to use such as an expensivehigh-frequency electric power source. A high frequency electric powersource of 400 HKz, which takes lower cost, can be used to produceradicals. The experimental results as shown in FIG. 3 were obtained withthe electric power source of 400 KHz. The frequency is not limited to400 KHz. Similar effects can be obtained within the range of 100 to 1000KHz. A high frequency electric power source of lower frequency than 1000KHz takes low cost. Accordingly, a plasma film-forming apparatus usingsuch a high frequency electric power source takes lower cost, incomparison with the prior art plasma film-forming apparatus.

[0034] Further, in the embodiment of this invention, polyfluoro ethylene(trade name-Tefron) is coated on the inner surface of the cleaning gasintroducing pipe 23. Accordingly, the radicals can be transportedthrough the cleaning gas introducing pipe 23 without the dissipation.Thus, the life of the produced radicals can be longer.

[0035] Sufficient cleaning rate can be obtained for SiNx film, even onlyby radicals. However, radicals are very directional. Accordingly, thereis the possibility that the films are not removed around the showerplate 5 and anode electrode 3, when only the radicals are used forcleaning. Accordingly, in the cleaning operation, Argon gas as inert gasfor sputter cleaning is introduced into the film-forming chamber 10besides NF₃ gas including fluorine radicals. A high frequency electricpower of 27.12 MHz frequency and 0.15 W/cm² electric power density isapplied to the introduced gases from the high frequency electric powersource 8 which is used also for film-forming.

[0036] Thus, the argon gas is electrically devided into Ar ions (Ar⁺)and electrons. The film-forming chamber 10 is cleaned both with thechemical reaction by radicals and with Ar ions sputtering. It can bemore uniformly cleaned, and the cleaning efficiency can be improved. TheAr gas is introduced into the film-forming chamber 10 through thecleaning gas introducing pipe 23 or through the film-forming gasintroducing gas 15. Insteads, it may be introduced through a specialpipe for spluttering gas.

[0037] Next, there will be described a second embodiment of thisinvention. SiO₂ film is formed in the same plasma film-forming apparatus20 as in the first embodiment. For example, SiH₄ gas and N₂O gas areused as a film-forming gas. The SiO₂ film is formed on the substrate 9in the same manner as the first embodiment.

[0038] In the cleaning operation of the film-forming chamber 10, NF₃ gascontaining fluorine radicals is directly introduced into thefilm-forming chamber 10 from the gas introducing pipe 23. The fluorineradicals reacts chemically with the SiO₂ film to be cleaned. Thus, thefilm-forming chamber 10 is cleaned.

[0039] Although the radicals are effectively introduced into thefilm-forming chamber 10, a sufficient cleaning rate cannot be obtainedfor SiO₂ film. Accordingly, Ar gas is introduced into the film-formingchamber 10. The high frequency electric power is applied to the Ar gasfrom the cathode electrode 4 by the high frequency electric power source8. Ar ions are produced. The film-forming chamber 10 is cleaned also bythe Ar ion sputtering.

[0040]FIG. 6 shows the comparison results of the cleaning of the SiO₂films among the cleaning only by the radicals (fluorine radicals), thecleaning only by the ions (Ar⁺) and the cleaning by the ions (Ar⁺) andradicals. When the film-forming chamber 10 was cleaned only by the ions,the high frequency electric power was applied to the cathode electrode 4at the frequency of 27.12 MHz and the power density of 0.67W/cm². Whenthe film-forming chamber 10 was cleaned by the radicals and ions, thehigh frequency electric power was applied to the cathode electrode 4 atthe same frequency as that of the cleaning only by the ions, and at thehalf power density of that of the cleaning only by the ions.

[0041] The cleaning rate of the cleaning operation only by the radicalsare low. However, that of the cleaning operation by combination of theradicals and ions is substantially equal to that of the cleaningoperation only by the ions. The required power of high frequency in thecleaning operation by combination of the radicals and ions is about halfof that in the cleaning operation only by the ions. Accordingly, theplasma damage to the shower plate 5 can be reduced, and so the showerplate 5 can be prevented from being deteriorated.

[0042] Next, there will be described a third embodiment of thisinvention. Parts in this embodiment which correspond to those in thefirst and the second embodiments, are denoted by the same referencenumerals, the detailed description of which will be omitted.

[0043]FIG. 3 shows a vertical cross-sectional view of a plasmafilm-forming apparatus 30 according to this embodiment. FIG. 4 shows across-sectional view taken along the lines IV-IV in FIG. 3. It is usedfor a large-sized substrate.

[0044] In the first and the second embodiments as shown in FIG. 2, theradicals are introduced laterally into the film-forming chamber 10.Accordingly, portions nearer to the outlet of the gas-introducing pipe23 are sooner cleaned. When the size of the substrate 9 is about 400mm×500 mm, there is no problem. However, when the size of the substrateis large as 730 mm×920 mm, the cleaning rate is generally lowered. Thefilm-forming chamber 10 is large-sized for a large substrate. Thecleaning rates are considerably different between portions near to theoutlet of the gas-introducing pipe 23 and portions farther from that.Totally, the cleaning rate is lowered.

[0045] In this embodiment, a first cleaning-gas introducing pipe 33 a isconnected to one side wall 2 a of the film-forming chamber 10, andanother cleaning-gas introducing pipe 33 b is connected to another sidewall 33 b of the film-forming chamber 10, which is facing to the oneside wall 2 b.

[0046] The cleaning-gas is introduced into the film-forming chamber 10from the two outlets. As shown in FIG. 3, the first and secondcleaning-gas introducing pipes 33 a and 33 b are shifted from thecenters of the walls in opposite directions. The cleaning-gas is moreuniformly introduced into the film-forming chamber 10 than in the casethat the cleaning-gas introducing pipes 33 a and 33 b are connected tothe walls, facing to each other. Of course, they may be connected to thewalls, facing to each other.

[0047] The cleaning rate of the large film-forming chamber 10 with thearrangement of FIG. 4 is about three times as high as that in the casethat only one cleaning-gas introducing pipe 22 is connected to the oneside wall as in FIG. 2. The high frequency electric power source ofabout 100 to 1000 KHz for producing radicals, is simple in constructionsand small-sized in comparison with the micro-wave generator.

[0048] The price of the former is one third as low as that of thelatter. Accordingly, plural radical-producing sources can be easilyarranged, and the manufacturing cost is not so high.

[0049] While the preferred embodiments have been described, variationsthereto will occur to those skilled in the art within the scope of thepresent inventive concepts which are delineated by the following claims.

[0050] For example, in the above embodiments, NF₃ is used as thecleaning-gas. However, it is not limited to NF₃, but CF₄, C₂F₆, C₃F₃,CHF₃, SF₆ etc. may be used as the cleaning-gas. Inert gas for sputteringcleaning is not limited to Ar. Further, the film to be formed in thesubstrate or to be cleaned, is not limited to SiNx and SiO₂. Further,the high frequency power to be applied to the cathode electrode 4, isnot limited to the above frequency and to the above electric powerdensity. Frequency between 10 to 100 MHZ may be adjusted.

[0051] Electric power density between 0.03 to 0.7 W/cm₂ may be adjusted.

[0052] In the third embodiment, two cleaning-gas introducing pipes areconnected to the film-forming chamber 10. The number of the connectedpipes is not limited to two, and more than two. The wall connecting thecleaning-gas introducing pipe, is not limited to the side wall, and maybe upper wall or bottom wall, of the vacuum tank 2.

What is claimed is:
 1. In a cleaning method for a plasma film-formingapparatus in a film-forming operation wherein a film-forming gas isintroduced through a shower plate having numerous holes into afilm-forming chamber, the introduced gas is excited and forms a filmwith the chemical reaction on a surface of a substrate arranged in saidfilm-forming chamber, and in a cleaning operation, a cleaning-gascontaining radicals produced by exciting said cleaning-gas is introducedinto said film-forming chamber and cleans said film-forming chamber bychemical reaction of said radicals and removes materials to be cleaned;the improvement comprising introducing said cleaning gas containing saidradicals directly into said film-forming chamber.
 2. A cleaning methodfor a plasma film-forming chamber according to claim 1, including insaid cleaning operation, introducing inert gas into said film-formingchamber in addition to said cleaning gas containing radicals, excitingsaid inert gas to inert ions, and cleaning said film-forming chamberwith the chemical reaction of said radicals and with the sputtering ofsaid inert gas ions.